The formation mechanism of special globular surface grain during the solidification of laser surface remelted near beta titanium alloys
The formation mechanism of special globular surface grain during the solidification of laser surface remelted near beta titanium alloys
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激光表面重熔近β钛合金凝固过程中特殊球状表面晶粒的形成机制
DOI：
10.1016/j.commatsci.2021.110353
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发表时间：
2021
影响因子：
3.3
通讯作者：
Wang Jincheng
中科院分区：
文献类型：
--
作者：
Wang Yujian;Li Junjie;Yang Haiou;Ma Jiankai;Cui Dingcong;Gao Yuan;Wang Zhijun;Wang Jincheng
在激光材料加工过程中，熔池表面区域附近的冷却速度(R)和热梯度(G)远高于传统铸造条件下的冷却速度和热梯度(G)，这可能导致特殊的凝固组织。采用激光表面重熔实验和相场模拟研究了近β钛合金的表面显微组织。结果表明，熔池表面附近晶核的晶粒呈近球状，具有<1 0 0>取向的侧分支，这与铸造条件下的普通枝晶形态有很大不同。采用相场模拟的方法研究了这种特殊表面晶粒形貌的形成机理。结果表明，高冷却速率(R)和高垂直热梯度(G)共同作用决定了表面晶粒形貌。高r增加了过冷度，减小了界面能各向异性的影响，使枝晶形貌由针状向近球状转变。高g促使晶粒轮廓更接近球形，有利于鳍状侧分支沿<1 1 0>方向发育。此外，建立了不同热条件下表面晶粒形貌的选择图（RandG），可用于预测表面晶粒形貌。
During laser materials processing, the cooling rate (R) and thermal gradient (G) near the molten pool surface region are much higher than those in the traditional casting conditions, which may result in special solidification microstructures. In this study, the surface microstructure of near β titanium alloys was investigated by conducting both laser surface remelting experiments and phase-field simulations. It was found that the grains nucleated near the surface region of the molten pool exhibit near globular shape with <1 1 0>-oriented side branches, which are very different from the ordinary dendrite morphology in casting conditions. Phase-field simulations were used to detect the formation mechanism of such special surface grain morphology. It was illustrated that the surface grain morphology is determined by the combined effect of high cooling rate (R) and high vertical thermal gradient (G). The highRresults in the morphology transition from needle-like dendrite to near globular shape by increasing the undercooling and reducing the impact of anisotropy of interface energy. The highGpromotes the grain contour to be more close to globular and facilitates the fins-like side branches to develop along <1 1 0> direction. Furthermore, a selection map of surface grain morphology at various thermal conditions (RandG) was established, which can be applied to predict the surface grain morphology.